The use of power drive units for a wide variety of applications is well known. In some applications, it is desirable to provide both manual and powered driven movement of a drive shaft depending upon the requirements at a given point in time. However, with such dual drive systems, there is an inherent danger to the manual operator.
More specifically, if a powered input is activated while utilizing a manual input, the manual operator may be exposed to possible serious injury. This could occur, for instance, because of feedback of the powered input through the manual input due to the manner in which the two inputs are linked to the drive shaft. For this reason, it is important to provide a manner of protecting the operator from such harm.
In other words, human safety considerations require that concurrent manual/powered operation be rendered essentially impossible. By way of example, this is important in a door/pallet hydraulic drive unit of the type utilized in connection with cargo aircraft. In such application, there is usually provided a brake for the door and/or pallet requiring release prior to movement of the drive shaft.
For maximum utility, it would be desirable to have both manual and powered means not only for driving a shaft but also for releasing the brake or brakes. This would render it possible to have maximum versatility at all stages of use of the system. However, as previously noted, any such system must include a safety device capable of precluding concurrent manual/powered operation.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objects.